Quantifying the seed bank of an invasive grass in the sub-Antarctic: seed density, depth, persistence and viability

Abstract

A native to Europe, 'Poa annua' now has a cosmopolitan distribution and is invasive in the sub- Antarctic. As a major weed in temperate turf, there has been considerable investment in research of the species, but little is known about its ecology in the sub- Antarctic, particularly its reproductive ecology and population dynamics. We characterised the seed bank of this invasive species in the sub-Antarctic, by quantifying seed density, depth, persistence and viability. 'Poa annua' seed bank density was correlated with elevation, animal disturbance, soil wetness and soil depth, but most strongly with 'P. annua' cover. Seed bank density was greatest (132,000 seeds m⁻2) at low altitude coastal sites where 'P. annua' is abundant but declined with increasing altitude to <2600 seeds m2. Seed was most abundant within the top 3 cm of the soil and decreased with soil depth. Seed viability declined over time, from an initial viability of 81 to <3 % after 2 years in the soil. This study demonstrates that whilst 'P. annua' seed banks can be dense, the seed bank is shallow (<10 cm) with low persistence and viability. This first detailed study on the in situ seed bank profile of 'P. annua' in the sub-Antarctic helps us understand the distribution and persistence of this invasive weed and is essential information for the development and implementation of future management. These findings, such as low seed bank persistence, challenge current thinking about eradication or control feasibility in the region.